Fungal phytopathogens are a cause of severe economic losses in the agricultural and horticultural industries. Many different types of fungal phytopathogens have been described: these pathogens cause plant diseases such as damping-off, white-rot, brown-rot and root-rot. Such diseases can kill emerging seedlings, reduce plant vigor and adversely affect crop yields.
To minimize fungal infections, bedding-plant nurseries may grow seedlings in steam sterilized or chemically treated soils. However, such treatments also remove beneficial microorganisms from the soil, including microorganisms that would normally compete with soil fungi. In such cases, if a fungal pathogen is accidentally introduced, it may spread rapidly and produce widespread disease.
In agricultural settings, soils infested with phytopathogenic fungi may be unsuitable for growing certain crops. For example, soybean production in Michigan and in other soybean growing states is often severely limited by Phytophthora root rot caused by the fungus Phytophera megasperma (Filinow and Lockwood, 1985). Species of Pythium fungi are widespread in soils in parts of California, Washington State and Idaho. Pythium ultimum is the most common pathogenic species encountered and is associated with pre- and post- emergence damping-off of seedlings. This species is a serious pathogen of wheat, peas and chickpeas and other crop plants grown in these soils and in soils in other states and other countries (Trapero-Casas et al., 1990; Stanghellini and Hancock, 1970; Kraft and Burke, 1971; Westerlund et al., 1988). The use of chemical agents to control fungal phytopathogens is often not practical due to high costs, lack of efficacy and the emergence of resistant strains of the fungi. Additionally, the use of chemical fungicides is not desirable from an environmental viewpoint.
It is an object of the present invention to provide new biological control means of reducing fungal pathogen infection of plants.